SILVER CYANIDE. 323 



formerly accepted is found to be at fault. The result observed 

 agrees perfectly with that calculated, when this calculation 

 is based upon the hypothesis of a total conversion into mercuric 

 cyanide and potassium chloride in solution. Moreover, this 

 does not affect the reciprocal reaction between the two last salts 

 when in solution ; i.e. the formation of a double cyanide, which 

 will be discussed presently. 



8. A reciprocal action of this kind is easily shown between 

 potassium cyanide in solution, and solid mercuric iodide, which 

 enters into solution 



J[HgI 2 (solid) + 4KCN(1 equiv. =16 litres)], total solution, 



+ 97. 



The solution of the solid body takes place, in this case, with 

 a considerable disengagement of heat, on account of the heats 

 of formation of the double salts that are generated and remain 

 in solution. 



9. The formation of the mercuric oxycyanides from the 

 combination of the cyanide with the oxide may be mentioned 

 here. This combination is effected with disengagement of heat 

 (Joannis) 



i[Hg(CN) 2 (solid) + HgO = Hg(CN) 2 ,HgO (solid)] gives off 



+ 1*2. 



This oxycyanide, when heated, explodes, in consequence of 

 the combustion of part of its carbon by the oxygen which it 

 contains. 



8. SILVER CYANIDE. 

 1. Formation from the acid and base. 



Some experiments were made on the heat of formation of silver 

 cyanide. 

 (6) AgN0 3 (l equiv. = 16 litres) + HCN(1 equiv. = 4 litres) 



+ 1572, 

 from which is got 



J[2HCN (in solution) + Ag ? (precipitated) = 2AgCN 

 (precipitated)] gives off + 20'9. 



(6) AgN0 3 (1 equiv. = 16 litres) + KCN (I equiv. = 4 litres) 



+ 26-57, 

 from which is got 



[HCN (in solution) -f Ag 2 (precipitated) = 2AgCN 

 (precipitated)] gives off + 20*9, 



a value identical with the above. It is, moreover, almost the 

 same as the heat disengaged in the formation of silver chloride. 

 Again, we get from the above results : 



|[2HCN (liquid) 4- Ag 2 (precipitated) = 2AgCN -i- H 2 (liquid)] + 21'3 

 [ 2HCN (gas) + Ag 2 (precipitated) = 2AgCN + H 2 (liquid)] + 27'0 

 i[2HCN (gas) + Ag 2 (precipitated) = 2AgCN + H 2 (gas)]... + 22-2 



Y 2 



